Phosphites and Phosphates:When Distributors and Growe

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For many years foliarapplications of sulphurand some trace elementssuch as Zinc, Copper andManganese have been used incombatting plant pathogens.More recently it was alsoproved that e.g. MKP (MonoPotassium Phosphate) has afungicidal activity, not onlyMonoPotassium Phosphites!So where is the problem? Is itprimarily that the plant pro-tection industry, which isbeing subject to tough andexpensive regulation to mar-ket its products includingphosphite-based fungicides,is not happy with the plantnutrition industry declaringand registering phosphitebased products as fertilizers-generally at no cost and with-out any delay- even if theymay have more fungicidalproperties than nutritionalimpact at the prescribedapplication rate? The plantprotection industry may geteven more nervous when theaccompanying promotionalliterature for such productsdescribes them more as bios-timulants and fortifyingingredients or even plantprotectors than as simplesource of nutrients!

SOME BASICS ABOUTPHOSPHORUSPhosphorus is the chemi-cal element that has thesymbol P and atomic num-ber 15. A multivalent non-metal of the nitrogengroup, phosphorus is com-monly found in inorganic

There has been some confusion lately in Europe andNorth America, now spreading to other parts of theworld, over terms used for fertilizers and chemicals

containing phosphorus. Distributors and growers havebeen using phosphate fertilizers for many long years.They are familiar with formulations like single super

phosphate (SSP), triple super phosphate (TSP)diammonium phosphate (DAP) but also MAP and MKP

(Monopotassium Phosphate). All of them providephosphate derived from phosphoric acid (H3PO4). The

phosphate that plants use is in the form HPO4 andH2PO4, which is quickly converted in soil from

fertilizers. Recently, new terms are being used includingphosphorous acid (not phosphoric acid), phosphite (not

phosphate), and phosphonite or phosphonate. Unlikethe phosphoric acid that contains four oxygen atoms,

phosphorous acid (H3PO3) and the related compoundscontain only three oxygen atoms. Is that difference of

one oxygen atom very important? In fact a cleardistinction exists between Phosphoric acid and

phosphorous acid: the former is a plant nutrient and thelatter has primarily fungicide applications. It is thus very

obvious that claims suggesting that either compoundmay exactly fulfill the functions of the other are

misleading. Therefore, is the bottom line that on the oneside phosphates are what is needed for fertilizer but will

have no effect on plant diseases and on the other sidethat phosphites are useful in managing diseases but will

not provide plants with the phosphate they need? Maybenot so simple! New Ag International went to investigateamong suppliers and scientists to try sorting out what is

really true, untrue and partly true? Our findings: What istrue is that plants can absorb the phosphorous acid

compounds through roots and leaves. What is also trueis that plants are incapable of using DIRECTLY the

phosphorus acid as a nutrient source. What is partlytrue is that the phosphorous acid compounds can breakdown in the soil to available forms of P, but this process

is very slow and will not provide adequate P nutrition.What is untrue is that they can complement and even

replace phosphate fertilizers in all instances. And what isvery true above all is that a number of people from

various bodies entertain confusion in the market!

phosphate rocks. Phospho-rus is a component ofDNA and RNA and anessential element for allliving cells. Due to its highreactivity, phosphorus isnever found as a free ele-ment in nature. It is veryreactive and rapidly com-bines with other elementssuch as oxygen and hydro-gen. When fully oxidized,it is bonded with four oxy-gen atoms to form the wellknown phosphate mole-cule. If not fully oxidized,then hydrogen occupiesthe place of one oxygenatom and the resultingmolecule is called phos-phite. The most importantcommercial use of phos-phorus-based chemicals isthe production of fertiliz-ers, based on phosphates.In agriculture, an otherimportant use of phospho-rus-based chemicals is theproduction of fungicidesbased on phosphites.This is all very simple butit becomes confusing andmisleading when someweb literature of a compa-ny having pioneered theuse of phosphites (deriv-ing from Phosphorousacid) as fertilizer, in itsFAQ page, compares Phos-phorous to Phosphorus(what for?) and describesthe latter as A poisonousnonmetallic element of thenitrogen group, obtainedas a white, or yellowish,translucent waxy sub-stance, having a character-

rs alike could get confused!

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and phosphonites) play animportant role in agricul-ture as active ingredientsin fungicide materials. Thismarket was pioneered byBayer Cropscience withworld-famous brandsAliette and Fosetyl-Al.When the patent for thetrademark Fosetyl-Alexpired, several other fun-gicide manufacturers cre-ated phosphite-basedfungicides by simple for-mulation of phosphitewith potassium, ammoni-um, sodium, and alu-minum. Trademarks nowalso include, among othersProPhyt (sold by HelenaChemicals), Phostrol(Nufarm America), Phos-guard, , etc. Phosphitefungicides are first formu-lated as ethyl phosphonateby reacting phosphite withethanol to form the ethyl

phosphonate anion and analuminum ion as thecounter ion. The problem(see table 2) is that where-as some of the phosphitecompounds are labeled aspesticides, which requiredthe manufacturer/distrib-utor to spend the time andmoney to register the com-pound, others, in NorthAmerica but also in a num-ber of European countries(Spain, Italy, Germany,etc) are advertised andregistered as fertilizers,which of course bypassesthe expensive and timeconsuming registrationprocess, and are even nowtested in organic farmingproduction (e.g. on grapesin France, Germany, Italy)!These phosphorous acidcompounds, most of thembased on potassium phos-phites, although activeagainst the Oomycota andsome fungal diseases, areclaimed to provide phos-phorus nutrition to theplant. True, untrue, partlytrue? What is true is thatplants can absorb thesecompounds through rootsand leaves and once in theplant, the phosphorousacids compounds are verystable. What is also true isthat plants are incapable ofusing DIRECTLY the phos-phorus acid as a nutrientsource. What is partly trueis that the phosphorousacid compounds can breakdown in the soil to avail-able forms of P, but this

istic disagreeable smell.Which one would you useafter reading this andknowing nothing aboutchemistry?

PHOSPHITES PRIMARILY USED AS FUNGICIDESAs early as 1930, a studywas carried out to deter-mine the efficiency of vari-

ous phosphorus (P) con-taining compounds as fer-tilizers. It concluded thatPhosphite was a poorsource of nutritional Phos-phorus since plants treatedby phosphite grew weakly.Therefore at this timephosphite couldnt find aniche in the market as apotential source of plantnutrient. Fourty years later,phosphites returned to themarket when it was foundthat they were very effi-cient against the Oomycota(i.e. species of phytophtho-ra and pythium). Today itis well documented thatthe toxic effect of phos-phite to Phytophthoracomes from the activationof defense mechanisms inplants or by direct actionon this fungal-like organ-ism, and phosphorous acidcompounds (phosphite

process is quite slow andwill not provide adequateand speedy P nutrition.What is untrue is that theycan complement and evenreplace phosphate fertiliz-ers in all instances.

A RENEWED INTEREST ONPHOSPHITES AS PLANT NUTRIENTSINCE THE EARLY NINETIESWhat is also true is that theeffectiveness of phosphitesin controlling plant dis-eases has been hiding theirpotential as fertilizers.However, interest in thesubject was renewed whenLovatt (1990), now Profes-sor of Plant Physiology atthe University of Davis inCalifornia and the recentco-author of an article onthe topic (in BetterCrops/Vol 90, 2006, N4)with Mikkelsen (IPNI),discovered that P deficien-cy in citrus species causedchanges in nitrogen metab-olism. Through the appli-cation of potassiumphosphite the biochemicalresponse as well as a nor-mal plant growth wererestored. Furthermore,Lovatt showed that fruitset and yield of avocadowere improved whenpotassium phosphite wasapplied with foliar sprays.This work led to the firstcommercialization ofphosphite compounds as afertilizer. A product waspatented and sold underthe trademark Nutri-Phite(Biagro Western Sales Inc),which is potassium phos-phite, derived from phos-phorous acid, potassiumhydroxide, and the organictripotassium citrate. Thisproduct is sold as a P nutri-ent fertilizer for foliarapplication and is used in awide variety of field andhorticultural crops. The listof phosphite products that

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are available in the Ameri-can and European marketsand are sold as fertilizersnow includes tens of brandnames. All of them are for-mulated as alkali salts of

phosphorous acid and allare registered under thefertilizer laws. The possi-bility of registration ofphosphite as a P fertilizerin most European countr-ries is surely due to thepredefinition in the EU fer-tilizer laws that the compo-sition of a P fertilizershould be expressed interms of P2O5. This isbased on long establishedpractices, which report ele-ments in oxides, hence, thereporting of P as %P2O5. Therefore,although a fertilizer maycontain phosphite insteadof phosphate this wouldstill be conform to the lawif Phosphorus is declaredas P2O5 in the fertilizeranalysis!The funny and some-what confusing part of thephosphite story is thatwhereas some companiesprimarily in the fungicide

business logically registertheir phosphite basedproducts as fertilizer whenthey can do so, some othercompanies primarilyinvolved in plant nutritionregister some phosphiteproducts as .fungicides!Is this driven by the searchfor higher mark-ups? Mostof them will find them-selves disappointed as themarket is very crowdedand is increasingly pricedriven.

CONFLICTING EXPERIMENTAL RESULTSThe number of productsbased on potassium phos-phites, magnesium phos-phites, calcium phosphites,etc. wouldnt have mush-roomed in the market ifthere were no documentedpositive effects of phos-phite application on cropsand in particular if foliarapplication of such prod-

Table 1: Some products of the Phosphorus family used in agriculture

Name Symbol CommentsThe Phosphate FamilyPhosphorus P The chemical element.

Does not occur as a free element in naturePhosphoric acid H3PO4 Compound found in most phosphate fertilizers. Contains 32% PPhosphate PO4 Completely dissociated form of H3PO4Phosphorus oxide P2O5 Formula used to express the phosphorus content in fertilizers.

It does not occur as a free element in natureFinished Phosphate Fertilizers:Single Super Phosphate SSP Dry fertilizer containing about 19% P2O5Di Ammonium Phosphate DAP 18-46-0 dry fertilizerTriple Super Phosphate TSP 0-45-0 dry fertilizerMonopotassium Phosphate MKP 0-52-34 dry fertilizerMonoAmmoniumphosphate MAP 12-0-61 dry fertilizerAmmonium Polyphosphate APP 10-34-0 liquid fertilizer

The Phosphite family:Phosphorous acid H3PO3 Compound normally marketed as a fungicide. Contains 39% PPhosphonate, Phosphite, Phosphonite PO3 Completely dissociated form of H3PO3

Some phosphite derived productsAluminium Phosphite Only marketed as a fungicidePotassium Phosphite Marketed as a liquid fertilizer, e.g. 0-58-38, 0-30-20 or 0-24-16Magnesium & Calcium Phosphite Marketed as fertilizersAmmonium Phosphite Marketed as fertilizer, e.g. 11-35-0Various micronutrients Marketed as fertilizersphosphites (Zn, Mn)

Source: Various

Avocado is a crop where theapplication of phosphite as foliarsprays proved beneficial to fruitset and yield in the early ninetiesand helped relaunch thecommercialization of phosphitesas fertilizers.

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ucts had not proven morethan just a fungicide effect.Research from Lovatt andmore recently Abrigoclearly shows that foliarapplications of phosphitecan replace phosphate incitrus and avocado cropssuffering from P deficien-cy. In these and othercrops, such application hasproved to be beneficial tofloral intensity, yield, fruitsize, total soluble solidsand anthocyans concentra-tion. At the same timehowever, Lowatt andMikkelsen warn thatphosphite is most effec-

tive when the rate and theapplication are properlytimed to match the needsof the crop and they

underline that since phos-phite is chemically differ-ent from phosphate, thesedifferences must be takeninto consideration to avoidplant toxicity. Toxicity, thekey word for the anti-phosphites people? To behonest, toxicity of phos-phites is as well document-ed as their positive effects,if not more! The toxic effectand the additional expens-es associated to the use ofphosphites were indeedthe reasons why researchalmost stopped for manyyears!In 1975, problems wereencountered again on over750 ha of corn in southern

Michigan that was tracedback to a 9-18-9 liquid fer-tilizer containing phos-phite. The fertilizer waseither foliar applied orapplied in a band in con-tact with the seed. About40 litres/ha was used."Plants showed white, var-iegated streaking of theleaves in mild cases andspindly, rolled, yellowish-white leaves in severe toxi-city", said Lucas when hepublished the results ofinvestigations in 1979.Interesting, no such symp-toms were observed in1976 when the same mate-rial was used. More recently in 2003,ammonium phosphite (11-35-0) was compared withthe well known liquid fer-tilizer ammoniumpolyphosphate (10-34-0) asa starter fertilizer on cottonon irrigated and non-irri-gated sites in South Geor-gia by Dr. Glen Harris,UGA-Tifton. Both materi-als were applied at 12 gal-lons per acre (slightly lessthan 100 litres/ ha) in a 2x2band at planting andapplied on the surface. The

Table 2: From Fungicides to Fertilizers: The marketing of some products with phosphorous acid & phosphites as active ingredient

Product Company Country Active ingredient Marketed as

Aliette Bayer Cropscience Germany Fosetyl-Al* FungicideNutri-Phite Biagro Western Sales USA Phosphites & organic acids FertilizerEle-Max Helena Chemical USA Phosphorous acid Foliar FertilizerProPhyt Luxembourg-pamol USA MonoPotassium Phosphite Systemic fungicideNutrol Lidochem USA Potassium Phosphite Fertilizer and fungicidePhostrol NuFarm America USA Phosphorous acid Biochemical pesticideAgrifos Liquid Fert Pty (Agrichem) USA MonoPotassium Phosphite FungicideFoli-r-fos 400 UiM Agrochemicals Australia MonoPotassium Phosphite FungicideFosphite Jh Biotech USA MonoPotassium Phosphite FungicideLexx-a-phos Foliar Nutrients Inc USA MonoPotassium Phosphite FungicideTrafos line Tradecorp Spain Potassium Phosphite Fertilizer & defense stimulatorPhytosK Valagro Italy Potassium Phosphite Biostimulant (registered as EC Fertilizer)Phosfik line Biolchim Italy Phosphorous acid EC fertilizerFosfisan, Vigorsan, etc Agrofill Italy Potassium Phosphite Defense Stimulator (registered as fertilizer)Geros-K L-Gobbi Italy Potassium Phosphite EC fertilizerKalium Plus Lebosol Germany Potassium Phosphite EC fertilizerFrutoguard Spiess Urania Germany Potassium Phosphite EC FertilizerFoliaphos** Plantin France Potassium Phosphite EC Fertilizer

*: Fosetyl-Al is an aluminium phosphite. **: not sold in France. Source: New Ag International database & others.

The effectiveness of ammonium phosphite application as a starterfertilizer for cotton needs further study.

Citrus is also a crop where some good results have been achieved withfoliar sprays of phosphites but there is no definite certainty that suchresults can be replicated every time.

symptoms of phosphitetoxicity were evendescribed as very similarto glyphosate damage,which prompted Monsan-to in 2005 to issue againreports and releases stipu-lating that glyphosate wasdegraded into inorganicphosphates/phosphoricacid in the soil and theenvironment, not phos-phites or phosphorousacid as suggested by

Whiley already 10 yearsbefore.

A NEED FOR A BETTER LEGISLATIONAND TRANSPARENCY ON LABELS?In Europe, the most recentfindings published in 2006by the Institute of PlantNutrition and Soil Scienceand the Institute of Ecolog-ical Chemistry and WasteAnalysis, both located inBraunschweig, Germany,seem to well summarize

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ammonium phosphiteresulted in shorter plantsat the fourth true leaf stagebut no differences in leaf Pconcentration and no sig-nificant differences in yieldat harvest were observed.Therefore, conclusionsfrom this one-year testwere ". . .inconclusive andthe effectiveness of 11-35-0(ammonium phosphite) asa starter fertilizer for cot-ton needs further study."

In 2004, farmers in south-eastern Alabama, southernGeorgia and northernFlorida have experiencedproblems on maize (toxici-ty) that were described asbeing related to the use ofa non-conventional fertil-izer material as a starterfertilizer. The material,ammonium phosphite,was used in a manner sim-ilar to ammoniumpolyphosphates. The

A N I N T E R V I E W W I T H

Both scientists are wellplaced to have a criticalview on the claims attrib-uted to phosphites. ProfDatnoff is the co-editor ofthe recently released refer-ence book Mineral Nutri-tion and Plant Diseasesand E.H. Simonne, anexpert in water and nutrientmanagement of vegetablecrops, is the co-author withL. Datnoff of a referencearticle published in 2005,entitled Phosphorous acidand Phosphoric acid: Whenall P sources are not equal.

Does phosphonate get con-verted into phosphate inplants and in soils?From what is in the litera-ture, some chemical conver-sion (slow) of phosphonateto phosphate may occur insoil by microorganisms andnon-enzymatic oxidativeprocesses since no enzymessuch as phosphonite oxidaseor phosphate reductase areknown to occur. This leavesthe conversion of phospho-nates into phosphate onceinside the plant with no doc-umented answer. However,Orbovic and his colleaguesrecently demonstrated thatcitrus seedlings supplied

with phosphonate or phos-phate grew equally well andthe P content of the leave tis-sue did not differ significant-ly between these twosources [Citrus seedlinggrowth and susceptibility toPhytophthora root rot areaffected by phosphate andphosphate sources of phos-phorus 2007, J. Plant Nutr.(in press)].

Is there any valid evidencethat phosphorous acid andphosphites improve plantgrowth?Phosphorous acid is knownto have a direct effect againstthe Oomycota (i. e. species ofPhytophthora and Pythi-um). This fungal-like groupof plant pathogens causes anumber of important plantdiseases. The mechanism ofaction of phosphorus acid isbelieved to be due to itsstimulating the plants natu-ral defense response againstpathogen attack. As such, bycontrolling disease youwould improve plant healthand consequently plantgrowth. There is some liter-ature also suggesting thatphosphorus acid or its saltspromotes plant growth evenin the absence of plant

Prof Lawrence E. Datnoff, Plant Pathology Department and E.H Simonne, AssistantProfessor, Horticultural Science Dpt, University of Florida

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pathogens (J. Plant Nutrition23:161-180).

Can some phosphate con-taining fertilizers such asMonoPotassiumPhosphatehelp control somepathogens?It is widely reported in theliterature that balanced andadequate fertility for anycrop reduces plant stress,improves physiological func-tion, and decreases diseaserisk. However, informationon P nutrition on plant dis-eases in the literature isinconsistent. Depending onthe P source, form, crop andplant disease, P can increase,decrease or have no effect onplant disease. That beingsaid, Reuveni and his collab-orators demonstrated thatfoliar applications of mono-potassium phosphateinduced systemic and localprotection of cucumber topowdery mildew develop-ment (Crop Protection19:355-361 2000).

Is there in the USA an offi-cial method of analysis thatallows laboratories to listseparately within the over-all Phosphorus content of acommercial fertilizer, the

proportion coming from thephosphate and phosphiteforms respectively?Not currently but if some-thing is to be found, it will bein looking at colorimetricmethods vs. spectrophoto-metric ones. Perhaps, ionchromatography could beused, too.

E. Datnoff

E. H. Simonne

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W H A T T H E Y T H I N K A B O U T P H O S P H I T E S

We offer to the growers acomplete range of twentyphosphites based productsunder the trademarkPHOSFIK, characterizedby the addition to the phos-phorus of one or more ele-ments (K, Fe, Cu, Mg, Mn,Zn, etc.), each formulaspecifically tailored to themost important crops(industrial, horticulturaland fruit trees), for foliar orfertigation application. By means of their peculiarchemical formulation thewhole PHOSFIK line isprocessed at our factory bya reaction that starts fromphosphorous acid reacting

with various componentsgenerating stabilized phos-phite salts. These phos-phites quickly penetrate thecrop tissues and provide anutritional action as well asa boosting coadjuvant effectto fungicides applied to con-trol the main fungal dis-eases. By enlarging the vascularsystem of the plant, ourproducts stimulate to theoptimum the assimilation ofphosphite ions and othernutrients carried in the for-mulation, allowing the plantto maximize phosphorusavailability along with a bet-ter nutritional balance,

Peter Marti, Export Director , Biolchim Spa, Italy

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growth and subsequentincreased yield. In the recent years, theefforts of our tech & salesteams helped us develop asubstantial presence in thekey Italian crop segments,namely grapes, citrus, stonefruits, olives and hydroponiccrops. At international level,I just want to mention ourmassive success in Germanywith PHOSFIK 3-27-18 +T.E. on strawberries andSolavit Mn, specifically tai-lored for potatoes to increaseyield and to promote homo-geneous tuber calibrationand quality parameters. Forus at Biolchim, the PHOS-

FIK line represents indeedthe very best answer to theneed of growers for a correctand innovative nutritionaland disease-control coadju-vating strategy in agricultur-al crops.

and reconfirm earlierresearch done elsewhereon maize: The detection ofdifferent phosphite concentra-tions in phosphite fertilizedmaize plants indicates thatthis P compound is wellabsorbed by plant roots. Afterphosphite foliar application,this compound was alsodetectable in all parts of maizeplants, which proves itsphloem and xylem mobility.The phosphite accumulationwas notably high in develop-ing corncobs. Phosphite isobviously stable within theplant metabolism process asonly small amounts appeared

Europe, most PotassiumPhosphite based products(using the raw material 0-58-38 at a usual dilutionrate of 50-60%) are regis-tered as PK fertilizers (e.g.Italian law 217, EU 2003regulation, etc.). Untilrecently there were no offi-cial analytical methods toindividuate the content ofPO3. For this reason, theinspection of such prod-ucts was always finding a0% content for PO4, whichis of course not acceptablefor a phosphate fertiliz-er! Today, an official ana-lytical method exists forPO3 that is used by inspec-tors when the presence ofPhosphites is indicated onthe label, which is not com-pulsory because the onlycompulsory mention forfertilizers is the P2O5 con-tent! Therefore a problemof transparency is stillthere!The market for phosphitesbased plant nutrition prod-ucts has grown during thepast years and it would

conclusions from Germanresearchers is a key pointindeed! Phosphite may goundetected by most agri-cultural testing laborato-ries that are set up to testfor orthophosphate. So far,approved techniques forfertilizer testing onlymeasures orthophos-phates. However, somenon-regulatory laborato-ries are switching to induc-tively coupled argonplasma technology for rap-id analysis of several ele-ments simultaneously.This technology has thecapability of measuringtotal P whether orthohos-phate, phosphite, or solu-bilized organic P. If thistechnique were used tomeasure total P, it couldcreate the impression thatplant-available P is higherthan it really is if some ofthis P was phosphite. Test-ing for the phosphite anionalone is tedious and expen-sive but it may be the priceto pay for a better trans-parency in the market. In

to be oxidized to phosphate.The reduced growth observedin phosphite treated plantswas especially evident underconditions of P deficiency.This could result from a sup-pression of the natural mech-anisms of plants to respond toP deficiency. These resultsshould be considered as anaspect of the German fertiliz-er law: in the future, the Pcontent of marketable mineralfertilizers is to disclose specif-ically in terms of solublephosphate or phosphiteinstead of generalizedP2O5, as hitherto.The last sentence from the

Corn is one of the most tested crops for effect of phosphite application,with contrasted and sometimes controversial results.

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certainly necessitate a bitmore transparency. Somesuppliers firmly believe inthe future of the marketwhile others are not soenthusiastic: it is a sort ofcommodity, we have oneproduct but it is not astrategic line for us, saysone Italian supplier whileothers, e.g. Biolchim (seeinterview) or Tradecorp(Spain) are expanding theirrange. The mood seems tobe as contrasted in NorthAmerica, with one big sup-plier of specialty plantnutrition products saying we are presently notinvolved in phosphites- wehave been presented witha number of opportunitiesbut have thus far chosen tostay with other foliar prod-ucts and biological diseasecontrol agents. The marketis pretty crowded and themargins are pretty thin fora number of these prod-ucts.The future will tell whowas right, especially afterthe lions share of the sup-

ply to most processors hasbeen taken over by Chi-nese manufacturers (cur-rently already supplying anumber of Italian proces-sors and a good part of thespanish ones) although itseems that the perform-ance of the cristalline rawmaterial coming from Chi-na (then dissolved byEuropean importers tomake a liquid finishedproduct) is not as good asthat of liquid productdirectly obtained throughsome different manufac-turing processes. In themeantime, distributorsand growers should beaware that phosphite fertil-izers, if not formulated andused correctly in consulta-tion with professionals,have a significant potentialto be phytotoxic whereas ifformulated and used cor-rectly they may well fit inan optimized crop cultiva-tion package, especially forselected cash crops.

C O U L D P H O S P H I T E B E A N E W F U N G I C I D E F O R O R G A N I C FA R M I N G ?

Potassium phosphite, alsocalled phosphonate, is asalt of phosphonic acidwith the formula K2HPO3.It should not be confound-ed with phosphates, nor

with the organophospho-rous insecticides which arealso called phospho-nates. Potassium phos-phite can be used as afungicide against oomy -

Bernhard Speiser and Lucius Tamm, FiBL, Switzerland

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cetes in various crops. In theearly 1990ies, it was exten-sively tested on organicallygrown grapevines inSwitzerland. It was effectiveagainst downy mildew(Plasmopara viticola), andblocked the disease up to 3days after infection. Phos-phite was mobile and verypersistent in plants andcould be detected in grapesharvested one year after thelast application. Analyses of53 wine samples reveiledthat the treatmentinevitably leads to phos-phite residues in wine, usu-ally ranging between 5000 10000 ppb phosphite. Phos-

phite residues were alsofound in other crops (e.g.potato, celery) treated withpotassium phosphonate.From a toxicological pointof view, these residues areof no concern. However,consumers of organic wineexpect to buy a naturalproduct, and we assumethat they would notapprove the presence ofsuch quantities of fungicideresidues in organic wine.Currently, potassium phos-phonate is not authorized asa fungicide for organicfarming in the EU, and wedo not recommend its use inthe future.

Bernhard Speiser Lucius Tamm

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